Merge pull request #508 from mronian/addsintegralimage

Adds Integral Image. Required for CENSURE in ImageFeatures

src/Images.jl

@@ -256,6 +256,7 @@ export # types
     thin_edges_nonmaxsup,
     thin_edges_nonmaxsup_subpix,
     canny,
+    integral_image,
 
     # distances
     hausdorff_distance,
@@ -284,7 +285,7 @@ Contrast/coloration:
 
 Algorithms:
 
-    - Reductions: `maxfinite`, `maxabsfinite`, `minfinite`, `meanfinite`, `sad`, `ssd`
+    - Reductions: `maxfinite`, `maxabsfinite`, `minfinite`, `meanfinite`, `sad`, `ssd`, `integral_image`
     - Resizing: `restrict`, `imresize` (not yet exported)
     - Filtering: `imfilter`, `imfilter_fft`, `imfilter_gaussian`, `imfilter_LoG`, `imROF`, `ncc`, `padarray`
     - Filtering kernels: `ando[345]`, `guassian2d`, `imaverage`, `imdog`, `imlaplacian`, `prewitt`, `sobel`

src/algorithms.jl

@@ -435,6 +435,8 @@ difftype{CV<:AbstractRGB}(::Type{CV}, ::Type{Float64}) = RGB{Float64}
 accum{T<:Integer}(::Type{T}) = Int
 accum(::Type{Float32})    = Float32
 accum{T<:Real}(::Type{T}) = Float64
+accum{C<:Colorant}(::Type{C}) = base_colorant_type(C){accum(eltype(C))}
+
 
 # normalized by Array size
 "`s = ssdn(A, B)` computes the sum-of-squared differences over arrays/images A and B, normalized by array size"
@@ -1956,3 +1958,22 @@ function shepp_logan(M,N; highContrast=true)
 end
 
 shepp_logan(N;highContrast=true) = shepp_logan(N,N;highContrast=highContrast)
+
+"""
+```
+integral_img = integral_image(img)
+```
+
+Returns the integral image of an image. The integral image is calculated by assigning
+to each pixel the sum of all pixels above it and to its left, i.e. the rectangle from 
+(1, 1) to the pixel. 
+"""
+function integral_image(img::AbstractArray)
+    integral_img = Array{accum(eltype(img))}(size(img))
+    sd = coords_spatial(img)
+    cumsum!(integral_img, img, sd[1])
+    for i = 2:length(sd)
+        cumsum!(integral_img, integral_img, sd[i])
+    end
+    integral_img
+end

test/algorithms.jl

@@ -146,6 +146,19 @@ facts("Algorithms") do
 
         @fact Images.test_approx_eq_sigma_eps(a[:,1:end-1], a[1:end-1,:], [3,3], 0.1) --> less_than(0.1)
         @fact_throws Images.test_approx_eq_sigma_eps(a[:,1:end-1], a[1:end-1,:], [3,3], 0.01)
+
+        a = zeros(10, 10)
+        int_img = integral_image(a)
+        @fact all(int_img == a) --> true
+
+        a = ones(10,10)
+        int_img = integral_image(a)
+        chk = Array(1:10)
+        @fact all([vec(int_img[i, :]) == chk * i for i in 1:10]) --> true
+
+        a = reshape(1:100, 10, 10)
+        int_img = integral_image(a)
+        @fact int_img[diagind(int_img)] == Array([1, 26,  108,  280,  575, 1026, 1666, 2528, 3645, 5050]) --> true
     end
 
     context("fft and ifft") do